Optimization of parameters for bio-ethanol production from sweet sorghum (Sorghum bicolor (L.) Moench) stalk juice and finger millet malt using Taguchi method

Abstract

Bio-ethanol is a promising renewable energy but its production is expensive from high cost of feedstocks. In this study, sweet sorghum (Sorghum bicolor (L.) Moench) stalk juice was investigated for bio-ethanol production. Most reports on bio-ethanol productions use commercial Saccharomyces cerevisiae as yeast. However, this study used finger millet (Eleusine coracana) malt with already high adaptation to local conditions and high economic viability as it is being utilized by the indigenous communities. Five sweet sorghum varieties of IESV-92001-DL (V1), NTJ (V2), 15233-IESV (V3), 92008-DJ (V4) and IESV-92028-DL (V5) were planted at 0°3'45.4644" North, 34°17'16.1052" South, in Kenya. °Brix content of juice was determined at 11th to 16th weeks after sowing. Highest °Brix for all varieties were at 15th week where V1 was highest at 22.07. V1 was then harvested for the juice. Factors affecting fermentation; temperature, time, pH and yeast to substrate ratio were optimized using Taguchi method and were obtained as 30 ℃, 48 hours, pH 5 and 5 g/L, respectively. Kinetics parameters of Vmax and Km were 0.35 g/L/h and 12.56 g/L, respectively. The optimized and kinetic parameters were within literature values and therefore finger millet malt has a great potential, as a substitute yeast source, in commercial bio-ethanol production. KEY WORDS: Bio-ethanol, Sweet sorghum juice, Taguchi method Bull. Chem. Soc. Ethiop. 2024, 38(1), 55-67. DOI: https://dx.doi.org/10.4314/bcse.v38i1.5